Driving a motor vehicle during dry, daylight hours is a relatively simple task requiring one merely to obey the traffic signals and keep the vehicle within the proper traffic lane as defined by the markings on the road. This relatively simple task becomes a particularly exasperating and often treacherous assignment when darkness and wet weather conditions prevail. Under these conditions, the usual night driving handicap of reduced visibility is augmented by the wet weather conditions, thereby making reflective road markings virtually imperceptible.
Road markings are generally made by using hot or cold traffic stripe paint, cold tape, or more durable materials such as epoxies or thermoplastics. Road markings generally come in two forms, long line stripes and transverse stripes. Long line stripes are typically four inches wide and include a solid line, an interrupted line, a pair of solid lines, or a solid line in combination with an interrupted line. The interrupted lines include a series of predetermined length traffic stripes separated by a series of predetermined length gaps. Interrupted lines are generally used with solid lines when center turn lanes (i.e., left-hand turn lanes in the United States) are applied, for example, to a three lane road. When two lines are used together, they are normally spaced four inches apart from each other. However, the spacing and dimensions of a traffic stripe can differ according to different country, state, country and city regulations.
Transverse stripes are normally short markings or legends. Transverse lines are normally considered to be stop bars, crosswalks, railroad crossing markings, words such as "ONLY", arrows, symbols and other markings and legends of that nature. Because cars often stop on transverse markings, these lines are usually directly subject to the power applied to the wheels of a car during acceleration. As a result, transverse lines generally experience more wear than long line stripes. Consequently, transverse lines are normally thicker than long line stripes.
Generally, when thermoplastic is used, stripes are applied in thicknesses of sixty to one hundred and twenty-five thousandths of an inch, and preferably, they are applied at ninety to one hundred and twenty-five thousandths of an inch. Also, reflective materials may be added on top of the traffic stripe to give it increased reflectivity at night. The reflective material primarily consists of glass beads applied on top of the traffic stripe after the stripe has been applied to the road surface.
Water does not drain from conventional road markings during wet weather conditions. As a result, when it is raining, a thin film of water will form on top of the traffic stripe and significantly reduce the retroreflectivity of the glass beads used therein. If a thick film of water forms on top of the traffic stripe, such as encountered in a heavy storm, the water will totally obscure the markings from view, thereby making them completely ineffective.
Because of the deterioration in traffic guidance conditions that occurs during dark and wet driving conditions, the incidence of traffic accidents increases and the usual smooth flow of traffic is impeded. Attempts have been made to eliminate these dangers by providing individual raised reflectors on the road surface, by using large reflective elements in road markings that protrude above the water film, and by forming profiled road markings having thickened transverse portions projecting above the water film.
One of the most widely used marking systems in the United States is an individual raised reflector, such as that available under the tradename Stimsonite.RTM. 948 or that shown in U.S. Pat. No. 3,332,327. The reflector generally comprises an approximately four and one-half inch by two and one-half inch marker that is raised one-half inch from the road and has sloped side surfaces. A reflective panel is disposed on each of the sloped sides of the marker and the entire top surface is then covered with a plastic or glass coating. As an example, these individual markers are placed every forty feet or so, such that one hundred thirty-two of them are used for each mile of road marking to help motorists when driving during dark and wet weather conditions. The markers are secured to the road using an epoxy glue or an adhesive, however, a problem with maintaining the markers on the road surface exists. For instance, on a hot summer day when the asphalt is especially soft, a heavy truck running over a marker will push it into the asphalt below the surface of the road. Heavy trucks also knock these markers off the road, thereby leaving a hole in place of the marker. In both instances, the effectiveness of the reflective marker is destroyed. The cost for such individual markers and their installation is also a significant drawback since using them on top of road striping can increase the cost of road markings by four hundred dollars per mile, or more, depending upon the spacing of the markers.
As an alternative to reflective markers, large glass beads have also been used to provide a profiled road marking having a pebble-like finish. In this system, produced by R.S. Clare & Co. Limited under the trade name Aquaflex.TM., large one to four millimeter glass beads and small crushed stones are spread on top of a binder coat layer and then coated with paint. Smaller conventional reflective beads are then dispersed over the painted line. Portions of the large glass beads are able to protrude above thin water films on the road surface thereby providing a reflective surface. However, using this type of large glass bead substantially increases costs, and since the larger beads are not universally accepted for road marking, approval on a state by state basis is required. Further, because of their size, the large glass beads do not adhere well to the road marking and have a tendency to be dislodged by traffic.
A further marking system used primarily in Europe is generally described in U.K. Patent Application 2,121,462. This marking system uses a relatively thick striping material extruded through a shaped die. The striping is applied in a line approximately one and one-half to three millimeters thick and at intervals of every ten to fifty centimeters. The die is raised to increase the outflow of the striping material and thereby form a wavy transverse ridge approximately five to ten millimeters thick. The striping material generally includes glass beads mixed therewith and additional glass beads are preferably sprinkled on top of the applied marking before it is completely hardened. The spaced ridges form a profiled marking having raised retroreflective surfaces at specified intervals that will project above the surface of a water film and thereby provide visible markings during dark and wet weather conditions. However, glass beads covering the raised ridges soon wear away due to the constant travel of traffic and, eventually, even the raised ridges themselves will wear down. Therefore, within a relatively short period of time, the increased visibility provided by the profiled marking is destroyed. In addition, the thickness of the marking prevents the water from properly draining from the road surface when the marking is applied as an edge line. This creates a pocket of standing water at the edge of the road surface that may cause vehicles to skid, thereby increasing the number of accidents.
U.S. Pat. No. 5,511,896 to Marcato, the entire contents of which are hereby incorporated by reference, uses an apparatus that applies a thermoplastic stripe to the road surface, and a layer of reflective material to the thermoplastic stripe. The apparatus also passes a rotatable wheel having a plurality of projections around its periphery over the thermoplastic stripe such that the stripe is deformed and spaced grooves are formed therein. An anti-adhesion agent, such as water, is preferably sprayed onto the rotatable wheel before the deforming step to prevent the still warm thermoplastic stripe from adhering to the wheel. An appropriate amount of water is sprayed on the wheel to cause a layer of reflective beads to adhere to the wheel and thereby prevent adhesion of the thermoplastic material. The plurality of grooves formed in the thermoplastic stripe assist in draining the water from the stripe during wet weather. However, drivers must still visually spot the line to determine its presence.
A strong need therefore exists for a durable and economical way to apply road markings that allow water to drain from the road surface, provide an audible signal to a driver when a vehicle passes there over, and have increased reflective properties so that they are visible at night during wet weather conditions.